Electrical light-transmission controlling arrangement



ELECTRICAL LIGHT-TRANSMISSION CONTROLLING ARRANGEMENT Filed Oct 15. 1947H. JAFFE Nov. 4, 1952 '5 Sheets-Sheet 1 X N 0 m. EE 20 6 88586 0058 5 7m2 mmE Q SNESE 2 9 459m INVENTOR. HANS. JAFF A ORNEY Nov. 4, 1952 H.JAFFE ELECTRICAL LIGHT-TRANSMISSION CONTROLLING ARRANGEMENT Filed Oct.15. 1947 5 Sheets-Sheet 3 Aw O EOP EMZUO Gmmu D G-E '0 0 INVENTOR. HANS.JA FF AT ORNEY Patented Nov. 4, 1952 ELECTRICAL LIGHT-TRANSMISSION CON-TROLLIN G ARRANGEMENT Hans J affe, Cleveland, Ohio, assignor to TheBrush Development Company, Cleveland, Ohio, a corporation of OhioApplication October 15, 1947, Serial No. 780,022

12 Claims.

1 The subject matter of this invention relates to arrangements forcontrolling the transmission of light and, while the invention is ofgeneral utility, it is of particular utility in arrangements forelectrically controlling the intensity of light transmitted or forelectrically controlling the color of light transmitted.

This application is a continuation-in-part of application for UnitedStates Letters Patent Serial No. 539,312, filed June 8, 1944, now PatentNo. 2,463,109, issued March 1, 1949, in the name of Hans Jaife andassigned to the same assignee as the present application.

There is a wide variety of applications for an arrangement forcontrolling the intensity of transmitted light or for controlling thecolor of the light transmitted. Light-controlling arrangements of thegeneral type under consideration may have many possible applications inphotography, recording of sound on film, etc. Arrangements of thegeneral type under consideration which have previously been availablehave been entirely unsuitable for many commercial applications. Suchprior devices have been characterized by one or more of the followingdeficiencies (a) A very low cross-section in the light path at the pointof control (73) High attenuation of light An insufficient range of lightvariation (d) An inability-to respond to highr-frequency variations of acontrol signal Thus, in the reproduction of television signals, it hasbeen heretofore proposed that a light valve, together with a localsource of illumination, be utilized to reproduce the televized picture,the light valve being controlled by the television video signals. Sucharrangements have not, however, been accepted commercially because ofone or more of the above-mentioned defects which has been present in allsuch prior systems.

It has been proposed to provide a light valve using a crystal substancewhich is piezoelectric and in which the controlling potentials appliedthereto are applied to provide an electric field parallel to the opticaxis of the system. Thus, in United States Letters Patent 2,277,007,granted on March 17, 1942, on the application of M. Von Ardenne there isdisclosed a television system in which such a crystal substance isutilized. The crystal substance which is proposed in this patent is zincblende or zinc sulphide. While arrangements of the type of the patent,in which the electric field applied to the crystal to control the lighttransmitted by the system is parallel to the optic axis of the system,are not subject to one of the above-mentioned defects, namely, to thedefect of a small cross-section, there are several other disadvantagesassociated with the use of crystals of zinc blende in a system of thetype under consideration. Specifically, only quite small crystals ofzinc blende are available commercially. Also, the transparency of zincblende is quite deficient for use in an optical system where arelatively wide range of Wave lengths of light are to be transmitted.Zinc blende has the property of highly attenuating signals at theshort-wave end of the visible spectrum so that the crystal is generallycolored when viewed in ordinary light. It would be desirable, therefore,to provide an arrangement for controllingthe transmission'of light'whichis not subject to one or more of the deficiencies oi the above-mentionedprior devices.

It is an object of the invention to provide an improved arrangement forcontrolling the transmission of light.

It is another object of the invention to provide an arrangement forcontrolling the transmission of light which is not subject to one ormore of the above-mentioned deficiencies of prior devices.

It is specifically an object of the invention to provide an arrangement,for controlling the transmission of light, which has a large crosssection in the light path at the point of control, low lightattenuation, and a high range of light control.

In accordance with the invention, an arrangement for controlling thetransmission of polarized light comprises a Z-cut plate of P-typecrystal material having its thickness direction approximately coincidentwith the path of the light and which is at least partially transparentto the light. Means are also provided, including electrode meansdisposed adjacentto at least one of the major surfaces of the plate, forapplying variable potentials across the plate of crystal material in thedirection of light travel, and, in a preferred embodiment of theinvention, this lastnamed means includes an electrode portion in thelight path which is at least partially transparent to the light topermit it to enter the crystal plate. An analyzer is provided for li htemerging from the plate.

As used in this specification, and in the appended claims, theexpression P-type crystal material is intended to mean primary ammoniumphosphate (NH4I-I2PO4) primary potassium phosphate, primary rubidiumphosphate,

the primary arsenates of ammonium, potassium and rubidium, isomorphousmixtures of any of these named compounds, and all otherpiezoelectrically active crystal materials isomorphous therewith.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawings and itsscope will be pointed out in the appended claims.

Fig. 1 of the drawing is a circuit diagram, partially schematic, of anarrangement in accordance with the invention for controllin thetransmission of light in accordance with sound waves to be recorded upona film; Fig. 2 is an exploded view of the crystal element and lensassembly of Fig. 1; Fig. 3 illustrates an embodiment of the inventionutilized to control the color of the picture reproduced in a televisionsystem; Fig. 4 illustrates an embodiment of the invention in which thearrangement is utilized as the lightcontrolling device in atelevision-picture reproducing system; and Fig. 5 illustrates a portionof the crystal plate of the Fig. 4 embodiment of the invention.

The P-type crystal materials to which this invention relates are allsuch that electro-optical properties are present for an electric fieldapplied parallel to the optic axis of the crystal. This permits anarrangement of the light beam approximately parallel to the optic axisand the latter parallel to the applied electric field resulting incomparative freedom from interference due to the nature birefringence ofthe crystal and enabling a large cross section in the light path at thepoint of control to be readily obtained. Also, these crystal materialsas a class have very desirable light-transmitting properties in thevisible portion of the frequency spectrum and certain of them, as willbe pointed out hereinafter, have high light-transmitting properties.Primary ammonium phosphate has its melting point near 190 C. and isabsolutely stable up to 120 C. Since this crystal has no water ofcrystallization it may be subjected to a. high vacuum for long periodsof time without detrimental effects.

All crystals which, by their symmetry, are piezoelectric can be expectedto show a linear electro-optic effect. A part of the electro-opticeffect is contributed by the elasto-optical effect due to thepiezoelectric deformation. In addition, however, there is a directelectro-optic effect which persists even if the piezoelectricdeformation is suppressed. The direct electro-optic effect is ofparticular interest inasmuch as it can be expected to be substantiallyindependent of frequency up into the ultra-short wave range ofvibrations. Its value, however, cannot be predicted from thepiezoelectric effect.

Certain of the P-type crystal materials have an amazingly high directelectro-optic effect and this fact was not known prior to my invention.Particularly efficacious arrangements involving plates of P-typeprimary-phosphate crystal material are described and claimed in mycopending application for United States Letters Patent Serial No.780,021, filed October 15, 1947, and assigned to the same assignee asthe instant application.

The nature of the electro-optic effect of an electric field appliedparallel to the optic axis of a P-type crystal material is such that thecrystal becomes optically bi-axial; that is, the propagation velocity ofa beam traveling par- 4 allel to the original optic axis is no longerindependent of the state of polarization. Thus light traveling parallelto the optic axis of P-type crystal materials is split up into twocomponents having planes of polarization at in respect to each other.After leaving the crystal material, these components again combine witha phase shift which is proportional to the voltage applied parallel tothe optic axis but which is independent of the thickness of the plate.

I have found the electro-optic effect of an electric field parallel tothe optic axis in primary ammonium phosphate crystals to produce a phaseshift of one-fourth wave-length at 4,500 volts for green mercury lightand have deter mined that the high value of about two-thirds of thiseffect is a direct electro-optic effect. The electro-optic effect inZ-cut plates, that is, plates cut from a crystal material and havingfaces oriented substantially perpendicular to the optic axis of thecrystal material, permit the construction of a light value of largecross section in the light path at the point of control and smallthickness with no need to compensate for the natural birefringence ofthe crystal. I have also found the direct electro-optic effect of afield parallel to the optic axis of a primary potassium phosphatecrystal to be even higher, specifically approximately 50% higher, thanfor primary ammonium phosphate which also makes primary potassiumphosphate eminently suitable for electro-optic purposes. The type ofelectro-optic effect found in Z-cuts of P-type crystals thus makes themparticularly useful for various devices for modulating the intensity oflight beams.

Referring now to Fig. 1 there is shown an arrangement for controllingthe transmission of polarized light which includes a Z-cut plate ll) ofP-type crystal material in the path of the light and which is at leastpartially transparent to the light of a source II. It is evident thatthe thickness direction, or Z-axis direction, of the plate 10 is atleast approximately coincident with the direction of the light path. Theplate IE) will be seen to have the shape of a slice cut from a singlecrystal of the P-type crystal material. It will appear from thediscussion hereinabove that a slice of primary ammonium phosphate(NI-I4H2PO4) crystal, otherwise called ammonium dihydrogen phosphatecrystal, is a P-type crystal material well suited for this purpose inmany cases; light valves and similar arrangements or devices comprisingmore specifically such crystal slices are disclosed and claimed in theaforementioned application Serial No. 780,021, which issued as PatentNo. 2,591,701 on April 8, 1952. The Fig. l arrangement also includesmeans for applying variable potentials across the plate in the directionof light travel, this last-named means including an electrode portion I2in the light path which is at least partially transparent to light fromthe light source II to permit light to enter the plate I0. An analyzerI3 is provided for light emerging from the plate l0. While it ispossible to utilize the plate l0 to control light in a system in whichlight enters the plate from one side, is reflected from a reflectingsurface at the opposite side of the plate, and again leaves the plate atthe same face at which the light originally entered, a preferredembodiment of the invention, as illustrated in Fig. l, is one in whichthe light enters one face of the plate and leaves the opposite face ofthe plate. However, it is to be understood that the invention is notlimited to this illustrated type bf ,action v ,':['1- ,t analyzer l 3 ison the opposite side-ofthe lat u from source H- and, a collimating lens.I4 is provided for forming a beam having substantially parallel rayswhich is thereafter-polarized by means of a polarizing screen l5 andcaused to be incident upon the plate H]. A retarding plate [6 may alsobe utilized in the system.

A lens I3 is provided for focusing the light transmitted by the systemupon a film I! which is driven past the focal point by means of a motorl8 driving one of the two reels 20,, 2| upon which the film is Wound.The above-mentioned means for applying variablepotentlals' acrossthe-plate l comprises the light-transparent electrode l2, upon one faceof the plate [0, and a light-transparent electrode 22 on the other facethereof,

together with a microphone. 23, connected to the input circuit of anamplifier 24, the output circuit of which is, in turn, coupled toelectrodes I2, 22.

One possible optic orientation'of the various elements of the Fig. 1arrangement is illustrated in Fig. 2. This shows the polarizer l andanalyzer I3 in crossed position with the X, axis of the crystal plate [0at 45 to the analyzer'position. In terms of the X, Y, Z coordinatesystem, a field parallel to the Z-axis will produce an expansion orcontraction along the X-axis and the opposite action, as the case may bealong the Y-axis, as explained in more detail in the above-mentionedparent application. Fig. 2 also illustrates a retardation plate I6Withthe orientation of the slow ray parallel to the X-direction of thecrystal Ill.

In considering the operation of the arrangement of Fig. 1, it. will beseen' that, in the absence of an applied voltage to electrodes I2, 22and in the absence of retardation plate Hi, the

system does not transmit any light. On the other hand, if potentials areapplied to electrodes 12, 22 sufficient to produce wave phase differencein the two optical components of polarized light transmitted by theplate l0, maximum light-intensity is passed by thesystem and is incidentupon'the film ll. This is true regardless of the polarity of thepotential applied to the electrodes I2, 22 and, for this reason, an ACsignal applied to the system would produce frequency doubling. It is toprevent this frequency-doubling effect that the retardation plate It isprovided. The retardation is in the nature of an optic bias andpreferably a retardation of A, wave-length is utilized as it provides asymmetrical increase and decrease of transmitted light intensity withthe application of an alternating voltage to electrodes I2, 22.Therefore, with the complete arrangement illustrated, sound signalsincident on microphone 23 are amplified in amplifier 24 and applied tothe electrodes 12, 22 each of which is (partially) light transparent.Light from the source H is collimated by the lens 14 toprovidesubstantially parallel rays which are-polarized by the polarizer I5.These rays are thereafter retarded by the plate l6 and the lightemerging from plate 16 is incident upon the plate 10. The light withinthe plates l6 and I0 effectively has two components each of which isplane-polarized, the planes of polarization of the two components beingat 90 to each other. These two components travel at different velocitiesthrough the plate 10, depending upon the potentials applied betweenelectrodes I2 and 22. Therefore, upon emerging, these two components mayhaverelative phase values dependent upon the potential which is applied,between electrodes and, 22,

and-these-components. combine to produce a resultant ellipticallypolarized beam. This emerging beam is transmitted through analyzer l3 toa degree depending on the value of its component taken parallel to thevibration direction of the analyzer. The intensity passed depends on thesumof the retardations in the fixed retardation plate [6 and'crystalplate [0 according to the equation I=Imax sin tr, where 6 is the totalretardation expressed in fractions of a wave-length. This retardationshows that for a fixed bias retardation of Wave-length, which may besupplied by retardation plate IS, the light; intensity will increasewith a positive retardation in crystal plate I0 and equally decreasewith a negative retardation, thus providing a symmetrical modulation.Light which is: transmitted through analyzer I3 is concentrated upon thefilm ll by the lens l9. Accordingly, therefore, the light incident uponthe film l"! varies in accordance with the sound variations. which arepresent at microphone 23. Hence the arrangement of Fig. 1 and in likemanner the other arrangements described and illustrated herein, may betermed light valves.

In place. of, orin addition to, the transparent electrodes [2 and 22, awire grid of very fine mesh maybe used. Such a grid is illustrated inFig. 2 at the reference numeral 25.

In Fig. 3 there is illustrated a color-television system utilizing anarrangement in accordance with the invention for controlling thetransmission of polarized light, specifically, for controlling the colorof the light which is transmitted. Referring now more particularly toFig. 3, the system as illustrated comprises a receiver of thesuperheterodyne type. This receiver includes an antenna system 30, 3|connected to a radio-frequency amplifier 32 of one or more stages, towhich is connected in cascade in the order named, as oscillatormodulator 33, an intermediate-frequency amplifier 34 of one or morestages, a detector and A. V. C. source 35, a video-frequency amplifier36 of one or more stages, and an imagereproducing device 31. Aline-scanning circuit 38 and a field-scanning circuit 39 are coupled toan output circuit of detector 35 and have output circuits coupled,respectively, to the line-scanning plates 42, 43, and the field-scanningplates 44, 45 of signal-reproducing device 31. Image-reproducing device31 includes a conventional electron-gun structure 46 and a fluorescentscreen 41 and is provided with a suitable source of unidirectionalpotential 48 therefor, as illustrated. Automatic-amplification control(A. V. C.) potentials derived from unit 35 are applied to one or more ofthe tubes in radio-frequency amplifier 32, oscillator-modulator 33, andintermediatefrequency amplifier 34 in a conventional manner. Asound-signal translating apparatus 40 and loud-speaker 4| ofconventional design are and coupled to the oscillator modulator 33,wherein they are converted into intermediate-freamplified in theintermediate-frequency amplifier 34 and delivered to the detector 35.Modulation components of the signal are derived by the detector 35 andare supplied to the video-frequency amplifier 36 wherein they areamplified and from which they are supplied in the usual manner to abrilliancy-control electrode of the image-reproducing device 31. Themodulation components of the signal derived by the detector 35 are alsoapplied to synchronizing-control circuits 38 and 39. The intensity ofthe scanning ray of device 37 is thus modulated or controlled inaccordance with the video-frequency voltages impressed upon its controlgrid in the usual manner. Also, scanning potentials, developed in theline-scanning circuit 38 and field-scanning circuit 39, are applied tothe scanning elements of the image-reproducing device 3'! to produceelectric scanning fields, thereby to deflect the scanning ray in twodirections normal to each other so as to trace a rectilinear pattern onthe screen 4'! to reconstruct the transmitted image. Sound signalsaccompanying the received television signals are reproduced in units 40and 4| in a conventional manner and the bias derived from unit 35 andapplied to the preceding receiver stages serves to maintain thesignal-input amplitude to detector 35 within a relatively narrow rangefor wide range of received signal intensities.

Referring now more particularly to the portion of the Fig. 3constituting the present invention, there is provided an opticalarrangement for controlling the color of light transmitted from thescreen 41 of the cathode ray tube to a viewing screen E2. This opticalsystem is generally similar to that of Fig. 1 and corresponding circuitelements have identical reference numerals while analogous circuitelements have identical reference numerals primed. Thus the opticalsystem of Fig. 3 includes, in consecutive order in the light path, acollimating lens [4 which is focused upon screen 41, a polarizer 15, abias plate It, a Z-cut plate of P-type crystal material I0, an analyzerl3 and a lens the screen ll of the cathode-ray tube 3'! to form an imageon viewing screen 50. The cathode ray tube 31 with its actuatingcircuits, the lens 14, and the polarizer l5 constitute means forprojecting White or polychromatic polarized light along the generallyhorizontal light path provided by the illustrated optical system.Electrodes i2 and 22, which are at least partially transparent to thelight generated by the fluorescent screen 57 of the cathode-ray tube,are i also provided. The retardation plate Hi, however, has a differentfunction than the retardation plate IE of Fig. 1 in that it has a muchhigher retardation value. One preferred retardation value for the plate!6 is two Wave-lengths of light at the center of the spectrum of thelight output from cathode-ray tube 3l. In considering the operation ofthe arrangement of Fig. 3, it will be seen that, if no electric signalis applied to the electrodes I2, 22 and if the system is illuminatedwith white light, a deep-purple color will be transmitted to the screen50. If now a constant voltage of either positive or negative polarity isapplied between the electrodes I2, 22, the retardation occurring in thecrystal plate It] will add to or subtract from the retardation obtainedin the plate It thereby to produce a change of color of the lighttransmitted depending upon the polarity and amplitude values of theapplied potential. By a suitable choice of the applied posi- [9 forfocusing the image present on L tive and negative potentials, therefore,it is possible to get two spectrum distributions which, together withthe spectrum distribution obtained with zero potential across the plates[2, 22, can serve as three basic colors for use in a color-televisionsystem. Assuming a white light to be emitted by cathode-ray tube H, aphase shift in the system of 1100 millimicrons for no potential appliedto electrodes I2, 22, together with a phase shift of plus and minusmillimicrons depending upon the amplitude and polarity of the positiveand negative signals applied to the electrodes ['2 and 22, provides onepossible set of three basic colors. This 165 millimicrons retardationvariation can be obtained by applying potentials of about 5,000 voltsupon a plate of primary ammonium phosphate or by applying potentials ofabout 3,500 volts on a plate of primary potassium phosphate. Fortelevision purposes, a substantially square-wave signal is applied tothe electrodes I2, 22 from a potential generator included in detector35. Specifically potential values consisting of one negative and onepositive pulse, each lasting during a complete field period of thetelevision signal, and a zero pulse, also lasting for a third fieldperiod of the television cycle, are used. A signal for controlling thegeneration of control potentials for electrodes [2, 22 is trans mittedwith the television signal, and is detected and separated in detector 35and thereafter utilized to generate proper control signals. Thus, in thesystem described, the color of the image reproduced on screen 50 ischanged in three discrete steps by the application of three discretepotential values to electrodes I2, 22, each color being incident uponthe screen 50 for a complete field period.

Using the lens system I4, l9 shown in Fig. 3, the polychromatic imageformed on the screen 4! of the cathode ray tube appears, in the mannerjust described, as a series of inverted color separation images on theviewing screen 50. Each image element on the screen 50 is reconstructedfrom a group of light rays which originate at the corresponding imageelement on the screen ll and which are polarized by the polarizer l5.For the upper most image element on the screen i! there are shown inFig. 3 the uppermost and lowermost rays of the group of rays which, uponpassage through the lens system, converge to form the lowermost elementof the image on the screen 50. Fig. 3 shows likewise the extreme rays inthe vertical plane of the group of rays passing from the lowermostelement on screen ll to the uppermost element on screen 50. It will beobvious at once that, for the formation of a useful focused image on theviewing screen 50, not only must the lenses l4 and I9 have a gross shapesuch as to provide the desired focusing action, but also these lensesand the other elements therebetween must have surfaces which are groundand polished or otherwise treated to avoid the scattering and defocusingaction caused by minor surface irregularities and scratches. Thus thecrystal plate or slice W has two parallel electroded faces which aresubstantially plane, and the bias plate IS, the electroded crystal plate0 with associated controlling signal circuits, the analyzer i3, and thefocusing lens [9 together make up an arrangement for controlling thetransmission of polarized light rays constituting the image elements ina picture transmission system. When the aforementioned sequentialcontrol potentials are applied to the light valve, the analyzer l3selects sequentially from the polychromatic light scanning windings 6|,6|

:acrcpcz the wave lengths of a'plurality of discrete colorscorresponding to the plurality of discrete steps of control potentialacross the plate I 0. Then the focusing lens I9 and the screen 50 serveas means for utilizing the light emerging from the analyzer l3 toproduce pictures, the color of which may be changed by varying thecontrol potential steps.

In Fig. 4 there is illustrated anembodiment of the invention in whichthe light-controlling system is utilized tocontrol the intensity oflight 56 and an image-reproducing device 51. A linefrequency generator58. and a field-frequency generator 59 are coupled to an output circuitof detector 55 through'a synchronizing-signal separator 60, theline-scanning generator 58 and the field scanning generator 59 beingcoupled to line and field scanning windings 6'2, 62, respectively,associated with the image-reproducing device 51. A sound-signaltranslating apparatus 64 and loud-speaker 65 are coupled to an outputcircuit of intermediate-frequency amplifier 54. The stages or units 49,to 56, respectively, 58 to 62, respectively, and 64 and 65 are all ofconventional well-known construction so that a detailed illustration anddescription thereof is unnecessary herein.

Referring briefly, however, to the general operation of the systemdescribed above, television signals intercepted by antennacircuit 49, 5!are selected and amplified in radio-frequency amplifier 52 and arecoupled to the oscillator modulator 53, wherein they are converted intointermediatefrequency signals, which, in turn, are selectively amplifiedin intermediate-frequency amplifier 54 and delivered to detector 55. Themodulation components of the signalare derived by the detector 55 andthe video components thereof are applied to the video-frequencyamplifier 56, wherein they are amplified and from which they areapplied, in the usual manner, to a brilliancycontrol electrode 63 of theimage-reproducing device 51. The synchronizing-component output ofdetector 55 is applied, through the syn chronizing-signal separator 65,to generators 58 and 59. The intensity of the scanning ray of device 5'!is thus modulated or controlled in accordance with the video-frequencyvoltages impressed upon the control electrode 63 in the usual manner.Scanning waves are generated in the line-frequency andfield-frequencyscanning generators 58 and 59, which are controlled by thesynchronizing-voltage pulses applied from the detector 55, and areapplied to the scanning elements BI, Bl andBZ, 52 of theimage-reproducing device 51 to produce magnetic scanning fields, therebyto deflect the scanning ray in two directions normal to each otherinorder to trace a rectilinear scanning pattern and thereby reconstructthe transmitted image in a manner which will be explained in detailhereinafter. Sound signals, accompanying the received televisionsignals, aretranslated by apparatus 64 and reproduced by loud-speaker 65in a conventional manner. An A. V. 0. potential, derived from unit 5!,is applied to one. or. more of the stages of units 52,- 53 and 54 inordertomaintam the sig- .nal amplitude to detector '55 within'arelatively narrow range for a wide range of received signal intensities.

Referring now more particularly to the portion of the system of Fig. 4embodying the present invention,there is provided an optical systemwhich is generally similar to that of Fig. 1 and similar elements haveidentical reference numerals. Thus the system comprises, in thefollowing order, a light source H, a lens 14, a polarizer 15, a Z-cutplate of P-type crystalmaterial 15, an analyzer l3 and a lens [9' forfocusing the light transmitted by the system upon a screen 5?. Theretardation plate [6 has been omitted for the sake of simplicity fromthe Fig. 4 arrangement, but it will be understood that, although it isnot required, this plate can also be included. As in the otherillustrated embodiments of the present invention, electrode means,disposed adjacent to at least one of the major surfaces of theplate, isprovided for the application of signal potentials thereacross.Accordingly, the optical system of Fig. 4 also includes alight-transparent electrode 22, corresponding to the same element ofFig. 1, but the light transmitting electrode l 2 of Fig. 1 has beenmodified in Fig. 4 to provide an electrode l2 which is comprised ofminute individual portions of secondary-electron emitting material onthe plate i0 so that an electron gun which includes the controlelectrode 63 canproduce a charge image on the dielectric surface. Thiselectron gun includes acathode 68, control electrode 63, focusing'andaccelerating anodes 69 and Ill and a collector electrode H. The cathoderay tube 5'! includes the entire optical system mentioned above withinthe tube structure, the lenses l4 and I9 effectively comprising separatefaces of the envelope of the tube.

A portion of the disk I0 is illustrated in Fig. 5 and in this figurethere is shown in detail the plurality of transparent electrode portionsof electrode [2 which are provided on the face of plate l0. Theseelectrode portions may be proividedby sputtering thin individual silverglobules thereon or may be provided by first coating the surface ofplate IB' with a thin coating of silver and bythereafter lining thesurface in both directions witha sharp instrument to provideisolatedislands of the silver coating.

For a successful reproducing unit of the type under discussion, theimage charge on the image grid must be discharged during each scanningcycle. The charge image on the image grid may be discharged betweenscansions by any one of several arrangements and an arrangementhereinafter called a chasing-beam scanning apparatus is illustrated inFig. 4 for this purpose. The chasing-beam scanning apparatus includes anelectron-gun, comprising a cathode 8B and focus? ing anodes 8| and 82for directing a stream of relatively low-velocity biasing electrons uponelectrode. [2. of the image grid, and a chasing-beam scanningngenerator84, having output circuits coupled to scanningwindings 85 and 8B, forcausing the beam igeneratedby the chasing-beam gun to scan thesurface ofelectrodelZin a manner to be described more fully; hereinafter. Suitableoperating potentials are provided for the electrodes of cathode-raytube, 51 in a manner which is well understood in the art- Scanningsystems and image grids which are somewhat analogous to those utilizedinthe Fig. 4 embodiment of the inventionaredescribed in detail in UnitedStates Letters Patent 2,280,191granted on-April 21, 1942,

on the application of Rudolph C. Hergenrother.

The secondary-emitting characteristics necessary for the image grid arespecified in detail in this patent as are also the electron-guncharacteristics for the gun including cathode 68 and the imageerasinggun including cathode 80. These characteristics will not be repeatedhere.

Considering now the operation of the tube 51 of Fig. 4 as animage-reproducing tube, it is seen that the electron gun structurecomprising cathode B8 and the electrodes 63, 69, and I2 is similar tothat of a conventional image-reproducing tube except that thefluorescent screen of the conventional tube is replaced by the structureof plate In including the electrode I2. It is seen that the control grid63 of this electron-gun structure is connected as a conventionalimage-reproducing tube to the television receiver and its operation willbe considered during a scanning cycle of the television image startingwith the dielectric material of plate It] uncharged. It will be assumedthat the secondary-electron emission characteristic of the structureincluding plate l and electrode i2 is suitably chosen, as taught by theabove-mentioned Hergenrother patent, to provide the operationhereinafter described. Specifically, the dielectric material of theplate I0 is charged positively by the electron beam as set forth indetail in the Hergenrother patent. This results in a distribution of apositive electrical charge over the dielectric surface which includeselectrode l2 that is, it results in the reproduction of a charge imagewhich is the electrical replica of the received television image. Thischarge image remains on the dielectric surface of the plate [0 for anappreciable length of time.

Therefore, in the operation of the tube of Fig. 4, it is necessary toprovide some biasing arrangement to bring the surface of the dielectricmaterial, which is provided with the electrode l2, to a uniformpotential between successive scansions. If this is not done, the chargeover the entire dielectric surface approaches a constant maximum valueand the image disappears. This biasing may be effected by electricalleakage of the charge through the dielectric material of plate W or by abombarding of the dielectric surface which comprises electrode 12' withelectrons of sufficiently low voltage that the secondary-emission ratiois less than unity, causing the charge on the dielectric to fall to thecathode potential of this bombarding beam. This cathode potential mayhave any convenient value. Such a discharge arrangement is provided inthe Fig. 4 embodiment of the invention by the electron-gun structurewhich includes cathode 80. The dielectric surface, under the conditionsassumed, continues to charge negatively until it reaches the cathodepotential of the bias beam. This cathode potential may be made negativerelative to the collector electrode H by a value equal to thebiasing-beam voltage if the anode of the biasing-beam gun is connectedto the collector electrode 1 I. This allows the biasing beam to enter afield-free space. The electron gun 80, BI, 82 is sharply focused to ascanning beam and is scanned over the surface of electrode 12. This biasbeam is scanned in the same manner as the signal beam from cathode 68but the phase of the sawtooth field-scanning current is retarded bynearly a full cycle or advanced by a relatively small amount so that thebias beam follows, or chases, the signal beam by almost a full scanningperiod. Therefore, the charge image on electrode I2, due to the signalbeam 68, is retained at full intensity for almost the entirefield-scanning period. This leads to an ideal condition giving asubstantially completely flickerless image. Since it is impractical toutilize an arrangement in which the scanning beam of cathode Bil isfocused as sharply as that of the imageforming beam from cathode 68, itis necessary to have a gap of appreciable width, for example 20 lines,between the image-forming beam and the bias beam. This phase relationcan be obtained by advancing the phase, of the field-scanning current ofthe bias beam developed by the chasing-beam scanning generator 84, theequivalent of 20 lines relative to the field-scanning current developedby the generator 59. Under these conditions flicker can appear in only20 lines so that the resultant average flicker is extremelv low.

An arrangement for inserting the unidirectional component of thereceived television picture has not been illustrated for the sake ofsimplicity but this may be provided by any one of the arrangements whichare well-known to those skilled in the art.

In summary, therefore, it will be understood that the video-signaloutput of amplifier 56 is utilized to control the grid 63 to place acharge image upon the surface of plate [0 which includes electrode [2.The plate II] is included at a focal point in the optical system so thatan image of the light transmitted by the plate is focused on the screen61. This image, of course, depends upon the charge image which ispresent at the surface including electrode I2. This charge image iserased by the beam from cathode just before it is to be scanned again bythe beam from cathode 68 in order to place a new charge image upon thesurface which includes electrode [2. It will thus be seen that theembodiment of Fig. 4 is an arrangement for controlling the transmissionof polarized light, specifically light which has been polarized due toits passage through element IS. The system also comprises a Z-cut plateof P-type crystal material [0 in the path of the light, together withmeans for applying variable video potentials across minute individualportions of the plate Ill in the direction of light travel. Asillustrated in Figs. 4 and 5, this last-named means not only includesthe grounded, transparent electrode 22 adjacent to the right hand orexit surface of plate [0 and the electrode [2 adjacent to the left handsurface made up of conducting islands as described above, but alsoincludes means for scanning the left hand major surface of the plate [0with a modulated electron beam, the latter means being constituted bythe electron gun 63--'H, its scanning and brilliancy-control elements9l63, and the associated sweep, synchronizing, and video amplifiercircuits. The conducting islands of the electrode l2 form minuteindividual electrode portions in the light path, corresponding to theaforementioned minute individual portions of the plate ill itself, andthese portions are at least partially transparent to the light to permitlight to enter the plate I 0. The analyzer I3 is provided for lightemerging from the plate I0. The viewing screen 6! then serves as animage-forming surface for receiving and displaying the modulated lightprojected through the individual portions of the plate 10.

While there have been described what are at present considered to be thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention and it is, therefore, aimedin the appended. claims tolcover all "such changes and modifications asfall within the truefspirit and scope of the invention.

I claim: I

1. An arrangement for controlling thetransmission of polarized lightcomprising; a Z-cut plate of P-typ'e' crystal "material having itsthickness direction approximately coincident with the path of said lightand which is at least partially transparent to said light; means,including electrode means disposed adjacent to at least one of the majorsurfaces of said plate, for applying variable potentials acrosssaidplate in the direction of light travel; and an analyzer for lightemergingfrom said plate.

2. An arrangement for controlling the transmission of polarized lightcomprising; a Z-put plate of P-type crystal materialhaving'its'thicknessdirection approidmately coincident with the path of said light and whichis at least partially transparent to said light; means. for applyingvariable potentials facross said plate in the direction 'of light traveland including an electrode portion, disposed adjacent to one of themajor-surfaces of said plate, which is at least partially transparent tosaid light to permit said light to enter said plate and an electrodeportion disposed adjacent to the other major surface of said plate; andan analyzer for light emerging from said plate.

3. An arrangement for controlling the transmission of light comprising:a polarizer in the path of said light; a Z-cut plate of P-type crystalmaterial, disposed in said path following said polarizer with thethickness direction of said plate approximately coincident with saidlight path, and which is at least partially transparent to said light;an analyzer in said path following said plate; and means, includingelectrode means disposed adjacent to at least one of the major surfacesof said plate, for applying variable potentials across said plate in thedirection of light travel.

4. An arrangement for controlling the transmission of light comprising:a polarizer in the path of said light; a Z-cut plate of P-type crystalmaterial, disposed in said path following said polarizer with thethickness direction of said plate approximately coincident with saidlight path, and which is at least partially transparent to said light;an analyzer in said path following said plate; and means for applyingvariable potentials across said plate in the direction of light traveland including electrode portions in said path disposed adjacent to bothsides of said plate and which are at least partially transparent to saidlight.

5. An arrangement for controlling the transmission of polarized lightcomprising; a Z-cut plate of P-type crystal material having itsthickness direction approximately coincident with the path of said lightand which is at least partially transparent to said light; means,including electrode means disposed adjacent to at least one of the majorsurfaces of said plate, for applying variable potentials in the audiofrequency range across said plate in the direction of light travel; andan analyzer for light emerging from said plate.

6. An arrangement for controlling the transmission of polarized light ofa relatively wide range of wave-lengths comprising: a Z-cut plate ofP-type crystal material having its thickness direction approximatelycoincident with the path of said light and which is at least partiallytransparent to said" light; means; including electrode means disposedadjacent "to at least one of the major surfaces of said plate, forapplying potentials, variable in a plurality of discrete steps; acrosssaid plate in the direction of light travel; and an analyzer for lightemerging from said plate to-provide light in a plurality of discretecolors corresponding to said above-mentioned plurality of discretepotential steps.

7. An arrangement for controlling the transmission of polarized light ofa relatively wide range of wave-lengths comprising: a Z-cut plate ofP-type crystal material having its thickness direction approximatelycoincident with the path of said lightand which is at least partiallytransparent to said light; means, including electrode means disposedadjacent to at least one of the major surfaces of said plate, forapplying potentials, variable in a plurality of discrete steps, acrosssaid plate in the direction of light travel; an optical-bias plateincluded in-thepath of said light; and an analyzer for light which hasbeen transmitted through said Z-cut plate and through said bias plate toprovide light in a pluralityof discrete colors corresponding to theabove-mentioned plurality of discrete potential steps.

8. An arrangement for controlling the transmission of polarized lightcomprising; a Z-cut plate of P-type crystal material having itsthickness direction approximately coincident with the path of said lightand which is at least partially transparent to said light; means,including electrode means disposed adjacent to at least one of the majorsurfaces of said plate, for applying variable potentials across minuteindividual portions of said plate in the direction of light travel; andan analyzer for light emerging from said plate.

9. In a color-picture reproducing system, an arrangement for controllingthe transmission of polarized light of a relatively wide range of wavelengths comprising: means for projecting polarized polychromatic lightalong a light path; a Z-cut plate of P-type crystal material which hasits thickness direction approximately coincident with said path of saidlight and which is at least partially transparent to said light; means,including electrode means disposed adjacent to at least one of the majorsurfaces of said plate, for applying potentials, variable in a pluralityof discrete steps, across said plate in the direction of light travel;an analyzer for light emerging from said plate to select from saidpolychromatic light wave lengths of a plurality of discrete colorscorresponding to said above-mentioned plurality of discrete potentialsteps; and means for utilizing the light emerging from said analyzer toproduce pictures, the color of which may be changed by varying saidpotential steps.

10. In a television system, an arrangement for controlling thetransmission of polarized light comprising: means for projectingpolarized light along a light path; a Z-cut plate of P-type crystalmaterial which has its thickness direction approximately coincident withsaid path of said light and which is at least partially transparent tosaid light; means, including electrode means disposed adjacent to atleast one of the major surfaces of said plate and including means forscanning one of said major surfaces with a modulated electron beam, forproviding video potentials across minute individual portions of saidplate in the direction of light travel; an analyzer is for lightemerging from said plate; and an image-forming surface for receiving themodulated light projected through said individual portions of saidplate.

11. In a television system, an arrangement for controlling thetransmission of light comprising: means for projecting light along alight path; a polarizer in said light path; a Z-cut plate of P- typecrystal material, disposed in said path following said polarizer withthe thickness direction of said plate approximately coincident with saidpath of said light and which is at least partially transparent to saidlight; an analyzer in said path following said plate; means, includingan electrode disposed adjacent to each of the major surfaces of saidplate, for applying variable video potentials across minute individualportions of said plate, said electrodes including corresponding minuteindividual electrode portions in said path which are at least partiallytransparent to said light to permit light to enter said plate and aconductive electrode in the path of said light which is at leastpartially transparent to said light to permit light to emerge from saidplate; and an image-forming surface for receiving the light projectedthrough said individual portions of said plate.

12. A light valve for controlling the transmission of polarized lightrays constituting the image elements in a picture transmission systemcomprising a slice cut from a single crystal of a P-type crystalmaterial and having two substantially plane faces oriented substantiallyperpendicular to the optic axis of said crystal, lighttransmittingelectrodes adjacent said faces respectively, and an analyzer for lightemerging from said crystal slice.

HANS JAFFE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,002,515 Worrall May 28, 19352,109,540 Leishman Mar. 1, 1938 2,277,007 Von Ardenne Mar. 17, 19422,280,191 Hergenrother Apr. 21, 1942 2,312,792 Bamford Mar. 2, 19432,330,172 Rosenthal Sept. 21, 1943 2,493,200 Land Jan. 3, 1950 FOREIGNPATENTS Number Country Date 518,812 Great Britain Mar. 8, 1940

